Automatic telephone trunkinft system



A. M. MALMBERG. AUTOMATIC TELEPHONE TRUNKQNG SYSTEM.

APPLICATION FILED FEB 5,19%. RENEWED MAY 31; i919.

Pa'tente DeuBO, 1919. I

6 SHEETS-SHEET 1 4 a I i a I i g tlni luivail|cinln\llirlrlaluw W W W W gnaz-""- Patented Dec. 30,1919.

6 SHEETS-SHEET 3- wifmesg a5 A. M. MALMBERG. AUTOMATIC TELEPHONE TRUNKING SYSTEM.

APPLICATION-FILED FEB. 5,1916- RENEWED MAY 31.1919.

Patented Dec. 30, 191%}.

A. M. MALMBERG.

AUTOMATIC TELEPHONE TRUNKING SYSTEM. APPLICATION FiLED FEB. 5. T916. RENEWED MAY 31,1919- 1 26,680. Patentea Dec. 30,1919.

6 SHEETS-SHEET 5.

& TIIIIIIIT 1| A M. MALMBEHG.

AUTOMATIC TELEPHONE TR'JNKING SYSTEM APPLICATION FILED FEB. 5. 1916. RENEWED MAY 21,1919.

Patented Dec, 80, 1919.

6 SHEETS SHEET 6 J t a a a M i a n: lilo/lei ANDERS M. MALMBERG, OF CHICAGO, ILLINOIS, AESSIG'NOH, 'LU AUTDMATIC ELECTRIC COMPANY, OF CHEGAGG, ILLINOIS, A. CDRPGRATION' 033 ILLIEZ $pecifieation of Lettcrs'iatent.

Patented Heel 3o, rote.

Application filed February 5, 1916, Serial No. 76,208. Renewed May 81., 1919. Serial Ho. 301,127.

1/ '0 all whom it may concern:

Beit known that I, Animus lliliiinninio, a citizen oi the United States, and a resident of Chicago, county of Coolc, and. State of .lllinois, have invented certain new and useful improvements in Automatic Tolephone Trunking Systems, oi which the following a specification.

My invention relates to automatic telephone trunking systems and more particularly to those trunking svstems in which the talking circuit is completed over a di'f ferent path from that used in the selection of the called line. in these systems non numerical and numerical switches may be used to extend a connection to it called line; whereupon certain rum-numerical switches accessible to the called line are operated to connect with the calling line at some intermediate point in the connection, thereby completinga new connection between the two lines by a more directrouie, and malt ingit possible, accordi'ngrly to release certain switches used in the original connection to make them accessible to other calls.

The ob: er, of my invention to provide, in a system of the above character; an improved trunking arrangement whereby such a system may be adapted to serve a large number subscribere comprising a plurality of exchanges.

A further object oi my invention is the provision of improved circuits and trunking devices whereby the el'liciency of suclnasystem is increased and the amount of apparatus required is considerably reduced.

'lo acconmlish these and other useful objects my invention comprises the means hereinafter set "forth and claimed.

in the drawings Figures 1, 2 and represent diagmmn'iatically the layout of a telephone system embodying the principles of my invention. I

Figs. 4, 5 and 0 taken together show a complete circuit connection between a substation A and a substation A in the ahove system.

Referring to Figs. 1 2, and 3, these draw ings being); arranged in order with the'lines at the sides thereotin alinement, it will describe in a generalway theniethod oi carrying'out my invention. The system as outlined has a total capacity of 100,000 lines terminating in ten ollicez-i or exchanges of 10,000li11es each. In 1 I have shown one oi. these 10,000 line exchanges; in Fig. l have shown a second 10,000 line eX- change; and in F 3 l have shown a third 10,000 line exchange. While these exchanges are substantially alike, I prefer to show several oi them in order that the trunkingbetween michanges may be more clearly illustrated. l ollowingthis plan further I have shown in each 10,000 line exchange threedilijerent thousand line groups. Each thousand line group is made up oi rive two hundred line groups as shown, one such group being; represented at A and another at A. This is as far as the subdivision goes, the number of lines in the smallest group being determined the capacity of a connector groupwhich ininy system is two hundred lines.

I will first describe the method of trunking between a calling; substation A and :1 called substation A the two being in the same exchange but in dii'l'ereut thousand line groups.

Each substatiim is connected at the exchange to an individual rotary line switch C which, upon the initiation of a call, operates to select an idle secondary line. switch I). The secondary line switch D has a double bank, one level containing contact-s which are terminals oit runlr lines extend ingr to third selectors M- and the other level containing contacts which are terminals of trunk lines extending; a to tertiary line switches it, these trunk lines being also multiplecl in the banks otlhider switches O and l.

When operated by calling line, the sec- I ondary line switch l) selects an idle tertiary lmesuutch E which in turn operates to select an idle first selector H. The sub-I scriber at substatloniit may now manipulate his falling: device for the first digits of the desired number, which, since substation A" located in the first 10,000 line ex rhange, will be L thereby raising); the wipers oi the first selectm' until they stand opposite the first level. whereupon they are automatically rotated to select an idle'second selector K; A being" located in the third thousand line group the next digit called will be three. which raises the wipers of the second selector until they stand opposite the third level, whereupon they are selector M. The normal wires from the;

.group serving the first and second hun-' automatically rotated to select an idle third two hundred'line group of which substation A is one, are shown multipled 111 the banks of the first connector group, this tated automatically to select an idle connector N. The connector N, it should be explained, 1s provided with a separate haul;

for each hundred which it serves and a double set of wipers, the set rendered active depending on the level upon which the tlnrd selector wipers are restmg.

At this stage of the operation the finder switch F is set in motion and it rotates n11- til it finds the trunk extending 'from the i to Figs. 2

call, the line switch C'individual tothe callsecondary line switch D to the tertiary line switch E, which trunk, as has already been explained, is multipled in the banks of the finder switches F'and 0. connection may now be traced directly from the secondary line switch D, through the finder switch F to the third selector M, and the first and second selectors H and K may be dispensed with, these switches, being, in fact, disconnected at this time and made ac cessible to othercalls.

The subscriber at substation A may now operate his calling device to select the last two digits of the desired line, whereupon the wipers of the connector N are ralsed and rotated until they rest upon the normal contacts of the line extending to the desired substation A. The line switch C, individual to the line of substation A, is now operated and selects an idle secondary line switch D. The secondary line switch D then operates to connect with the third selector M. The called line being now directly connected to the third selector M, the connector N is no longer necessary and may be released together with the wipers of the third selector. A complete talking connection has now been established between substation A and substation A which may be traced as follows: substation A, line switch C, sec ondary li'ne switch D, finder switch F, relays of third selector M, secondary line switch D, and line switch C to suhstation A.

I will now describe briefly the trunking between a calling substation A and a called substation A, the two being located in separate 10,000 line exchanges. Referring and 3, upon the initiation of a,

ing substation A operates to select an idle D; which in turn operates to select an idle tertiary line switchv switch E; which operates in its turn to select an idle first selector H, all in a manner whlch has been described.

The called substation A is located in the third 10,000 line exchange and therefore the first digit of the number to be called is 3. li manipulating the dial at the calling substation in accordance with this digit the wipers of the first selector Il will be raised untilthey stand opposite the third level, whereupon. they will be rotated automatically to select an idle trunk extending to the distant exchange shown in Fig. 3 and terminating therein in a tertiary line I. which operates to select an idle second selector K. (Fig. is now set ilk motion and rotates until its wipers reach the terminal of the trunk line extending )j'nr the secondary line switch D to the ti. l ary lino switch l whereupon the first selector II is released and-a connection is established from the calling substation A through line switch C, secondary line switch I), finder switch 0, and over the outgoing trunk to the tertiary line switch 1 in the distant exchange, which, as before mentioned, has already operated to'select an idle second selector K. The

called substation A being located in the sec ondthousand line group, of the number will be 2; and, by operating the dial at substation A in accordance with this digit, the wipers of the second selector are raised until they stand opposite the second level, whereupon they are automatically rotated to select a trunk line leading to an idle third selector M. In the drawing, I have shownthe normal wires of substation A as extending to the third connector group, wherefore the third digit of the number may be either 5 or 6. Manipulating the dial at substation A in accordance with one of these digits, the wipers of the first selector M are raised until they stand opposite the corresponding level, whereupon they are rotated automatically to select an idle connector N. The finder switch F with which the third selector M is connected, is now set in motion and rotates until its wipers reach the terminal of the trunk line terminating in the tertiary line switch I, this and other trunk lines being multipled in the banks of the finder switch F and other finders. Adirect connection has now been established from the incoming trunk line, through the finder switch F, to the third selector M, and the second selector K may accordingly be released to other calls.-

The subscriber at substation A operate his calling device in with the last two digits of the desired number, whereupon the wipers of the connector N are raised and rotated until they rest upon the normal contacts of the line extend the second digit may now and madeaccessible accordance ingg, to the substation A The line switch C individual to the line of the called substation iii is'noiv operated to select an idle secondary line itch D which in turn is operated to locate and connect with the third selector M whereupon a direct path is established from the incoming, trunk line to the called substation A to the exclusion of the connector N which may be released and made accessible to other calls. The substation A and the'suhstation A are now connected over a direct path which may be readily traced without further explanation.

l have not specified the exact number of trunk lines between the various groups as the number will vary considerably in practice, but it is to he understoodthat a suflicient number of such trunk lines will be provided to handle the trafiic.

Referring now to Fig. l, theautomatic substation A comprises the usual receiver 2, transmitter 3, ringer 4 and condenser 5. Being an automatic substation it is also providcd with a suitable hnpulse sending mechanism for controlling the automatic switches,

which mechanism is represented diagrammatically by a )air of im )ulse sorin s G I) m b the dial the impulse wheel will sepa ate the impulse springs a nun'lher of tunes corresponding to the various digits in the nun her of the called lines.

Each substation such as A is connected at the exchange toan individual rotary line switch (J of well known type and construe tion. Mechanically these switches may be similar to the ones shown in the patent to Deitl No. 1,126,727. The wipers 33, 3 k, and

are intended to be rotated by the motor magnet whose circuit is controlled by the line relay 13. A line switching relay 1% is provided whose function it is to connect the lines 11, 12 to the wipers at the proper time and also to open. the energizing circuit of the line relay. and motor magnet. The wipers 34-, 35'normally rest upon a set of contacts similar to 36, 3 7, and 38 and it is understood that each line switch G contains a plurality of such sets, corresponding sets in a number of line switches being-in multipie and connected; to trunk lines extending tosecondary line switches such as D. I The secondary line switch D is similar to the primary line switch 0 except that it has a double bank of contacts and two sets of wipers,,both sets oeing adapted, under the influence of the motor magnet, to traverse theirrespectire hanks of contacts at the same time. But one set-of wipers, however, is rendered active" at; a-giren time; the set chosen depending u on the. operation or non-operation of the i'claylll which in turn depends upon whether the switch is being used by acalling or by a called line. Secondary line switches D (Fig. t) and D (Fig. (i) are substantially alike. Line switch l) as shown. is in use from the calling sub-v station A and has its wipers T9, 550 and 81 in. service, the other set 76, 1'7 and 78 being dead.

The active set of wipers is shown restingupon a set of contacts 85, ShandST,

connected a trunk line extending to a third selector M. It is understood that each scc-, ondary line switch D or D has a plurality of contact sets such as 82, 83 and 8t, each set being multipled to corresponding sets in the llzlllliSO) a number of other switches l) or D; and each secondary line switch I or I) also has a plurality of contact sets such as 85, 86 and 87, each of these sets beingmultipled in a'similar manner.

At t) (l ig. 6) is showna rotary line switch individual to the substation A". Line switch (3 is similar in all respects to line switch 0.

At E (Fig. 4) is shown a tertiaryline switch having wipers 118, 119 and 1'20. adapted to be rotated by motor magnet 93 under the control of line relay 90. A line.

switching relay 91 and a cutoff relay 92 are provided and will he described. The,

wipers 118, 119 and 120 rest nm'xnally. upon .March 3-1, 1906, to Keith, Erickson and Erickson,except that the circuits are modifled to enable the switch to be operated by impulses delivered over one wire and to en'- ablefimpulses so delivered to be repeated ahead after the selector H has performed its function. p v V The selector H comprises the usual .verth cal and rotarymagnets'lilfl and 131, for

L raising and rotating the wipers 156, 157 and.

158 through the medium of a shaft. (not 15 shownland a 'ifelease u'iagnct 1'28 torrcstor- 1 ing the wipers to tl'ieir noru'lalposition Ofi' 1 normal contacts l rfiand 146 and of? normal contact are closed at the first upward movement of the selector shaft and oil nor- 13C i in . arranged in horizontal rows or levels and,

since the system in question is a multi-office system, it to be understood that a certain level or levels will be used tor trunking calls in the same olliee while the other levels will he used torirunking calls to other oflices.

-The drawing shows two sets of contacts each set being in a different level. Contacts 162, 163 and 16-1 are inultipled to corresponding contacts in other selectors and are connected to a trunk line extending to the second selector K. Contacts 159, 160 and 161 are also multipled to corresponding contacts in other selectors and are connected to a trunk line extending to a rotary finder switch 0. There is of course, a plurality of sets of contacts in each level each set having multiples in other selector banks and a trunk line connected as described.

Referring to F 1g. 5, the second selector K is similar to the first selector H. It has,

however, tour wipers instead of three and a correspomlingl y increased number of bank contacts in a set. There are also circuit modifications which will be mentioned later. Zach level in the second selector bank has a plurality of sets of contacts, each set being multipled in the banks of other selectors and connected to a trunk line extending to a third selector M. Individual to each sec ond selector K is a battery B whose positive pole is connected to the multiple bank contacts associated with second selector K and located in the banks of finder switches such as F, and whose negative pole is connected to the wiper 256 of the second selector K.

The finder switch F has three sets of wipers (274282) adapted to be rotated in unison by the motor magnet 291 which is in series with the grouping relay 290, and is controlled by the test relay I might employ but one set of wipers on the finder switch 1* and arrange the various sets of ban kcontaets all in one level, but in view of the large number of such contact sets, I prefer to arrange them in several horizontal levels, each level having its own set of wipers. Iii-finding a certain set of contacts all the sets of wipers rotate. until they rest upon theyertical row in which is located the required set of contacts, one set of wipers ot' coin-so, being actually on the required set of contacts. 1 then select this set of wipers by means of the side switch wipers 283, 284

private magnet 320 normal positions. The private magnet 320 i in connection with the test relay 292 controls the side switch, whim-s 283, i284 and 285 in the well known manner. A calling bridge relay 30:2 is arranged to deliver impulses either to the vertical magnet or to the c0nnector N and also serves to feed talking battery to the calling line. An answering bridge relay 299 reverses the calling line for purposes ot' supervision 'a-ndalso serves to feed talking battery to the called line. A ringing relay 298 is provided for signaling the called subscriber. The relay 305 has a pair otisprings 364 and controlled by an escapement in such a manner that when they are separated by the energization of: relay 305 they will not again make contact until after two actuations of the relay 307 which controls the escapen'lent. A busy relay 312 i is provided and at the proper time connects a lead from the induction coil T to one side of the calling line. There are also provided a wiper cut-oil relay 310and a test relay 313, whose functions are sufficiently indicated by the names applied. The off-normal contacts 377 and v378, 373 and 374, and 370 and 371 areclosed by the first upward movement of the shaft. The oil normal contacts 370fand372are opened at the first upward movement of the shaft.

The bank contacts. are arranged in horizontal levels in the well known manner, each set of contacts being multipled'to corresponding sets in the same levelin other third selectors. Although there are ten different levels there are but five groups of trunks leading to connectors N, the adjacent; odd and even levels being tied together as shown. The drawing shows the first set of contacts (412, 413) in the first level and the first set of contacts (414, 415) in the second level, contacts 413 and 415 being tied together while contacts 412 and 414 are not. All the other sets of contacts in the first and second levels are connected in the same inanner and form terminals of trunk lines extending to agroup of connectors of which is one. Similarly corresponding sets of contacts in the third and fourth levels have their contacts such as 413 and 415 tied together and form terminals of trunk lines incense feeding talking battery and for ringing, the

addition of certain parts, and of certain cir curt nun'hhcations, which are necessary to enable the switch to operate in accordance with the principles or my invention.

The wipers l51-l5l are carried by a shaft (not shown) which may raised and rotated by means of the usual vertical and rotary magnets 4122 and The side switch wipeis M8, till, 450 are controlled by the private magnet 4:27 in the usual inanner. A release magnet provided for restoring the shaft and side switch wipers to their normal position. A. wiper switching relay ;:20 is provided whose operation or non-operation depends on whether the thirdselector wipers are resting upon the even or odd level of bank contacts. Associated with each connector N is a battery B whose negative pole is connected, in the third position of side switch wiper 440, one wire of the trunloline extending from the third selector banks, and whose positive pole is connected, through contacts of relay 4:20 to one of the test wipers 451 or Each connector N has 200 sets or bank contacts which are in multiple with correspondin sets in other connectors of the same group and which form terminals of normal wires. extending to individual line switches such as C or C. These bank contacts are arranged in two banks each having 100 sets of contacts. In the drawing contacts 457 and 458 represent the first set of contacts of the; first level of the first bank, while contagtsdofi and $56 represent the first set of contacts of the first level of the second" bank. 'l he two sets of wipers and e54, and 4:51 and 4:52 are moved simultaneously to engage correspoiuling contacts in their. respective hanks, but only one set of wipers is rendered eli'ective at a given time as will be explained more fully in the detailed de scription of the operation.

At 13 (Fig. 5) I have shown. a battery having one terminal grounded, the other terminal being extended to Figs. 4 and (3. At l is shown an interrupter ior intermittently energizing the ringing relay 2.08. A busy n'iacliine S and a transformer l. are providcd for the purpose or indicating to" a calling subscriber when a. called line is busy.

The switches 0 (Fig. 4;) and P (Fig. 5) are, associated respectively with outgoing and incoming trunks extending to and from other1(),000 line cxchz'inges. Considering first the switch l itis most nearlylike the tertiary line switch E in circuit ar rangenient'. The wipers 212,213 and 214-. rest normally upon a set of contacts such as contacts 2; 5 216 and 217, these contacts be- 'ing terminals of trunk lines extending to second selectors such as it. The test con: tact of each set. as shown in the drawing, is in multiple with corresponding txst contacts in the first hank level. of the first selector H, whereby it is seen that a group of line switches such as P with their banks 1nultiplodare given access to the same group of second selectors such as K as the first selector H has access to through its first bani:

level. The incoming trunks are multipl ed in the banks of the finder switches F as shown.

' also form multiple terminals of the trunk lines extending from the banks of the secondary line switches D to the banks of the finder switches F.

At li- I have shown a repeater which may be of any suitable type and construction.

While a repeater is not absolutely essential and has been omitted from. the description 01 the general trunking scheme, it is very desirable in practice and I have therefore included it in the detailed description and in the circuit drawings.

I belive it has been made clear that the line and finder switches shown herein are of the single motion, rotary type in which the wipers have no normal position, although it is of course perfectly possible to practice my invention ith switches of other types.

In order to, avoid any erroneous conclu' sion as to the operativcness of the rotary switches with which I have chosen to illus tratc my invention it should be explained that the wiper connections are made byincans of an approved collector ring arrangen'ient so as to allow a movement of the wipers in one direction only.

Having given a general description of the apparatus, I will now proceed to a detailed description of the-operation.

Referring to Figs. 4, 5. and 6, arranged Y in order with the lines at thee nds thereof in alineinent, it will be explained how a subscriber at substation A may establish a talklocated in a distant exchange and also how such a connection may be established in the reverse direction.

It will.furthermore be explained how the connections mentioned above may be released and the apparatus restored to normal.

\Vhen the subscriber at substation A raises the receiver from the hook to initiate a call, a circuit is. con'iplcted for the line relay 13 of the line switch C, said circuit extending from the round at l throu h normall H 5 I" closed contact springs '21 and :22, over line 11 to substation A, whence it returns over line 12, through normally closed contact springs 19 and 18, winding of line relay 13 to battery. Upon the energization of the line relay circuits are completed for the line switching relay ,1-1 and for the test wiper 3-1 which may be traced as follows: ground at G, contact springs '29 and 30, winding of line switching relay. 1+, contact springs 16 and 17, winding of motor magnet 15 to battery. Test wiper 31, contact springs 25 and 21, contact springs 27 and 28, contact springs 16 and 17, winding of motor magnet 15 to battery. Current flowing in the former circuit is insutiicient to effectively energize motor magnet 15 for the winding of relay 1% has high resistance. The operation now depends on the condition of the test contact upon which the test wiper is resting. If the test wiper is resting upon the test contact of an idle trunk the line switching relay will pull up at once and the motor magnet will not be operated at all; but if the test wiper is resting upon the test contactot a busy trunk, it will find ground potential and a direct short circuit will exist around the wind- I ing of the line switching relay 14. In this case the line switching relay 11 isjinoperative while the motor magne 15 is effectively energized. Since the motor magnet 15 interrupts its own circuit it continues to attract and retract its armature, thereby rotating the wipers 33, 31 and 35, until the test wiper 31 arrives at the ungrounded test contact of an idle trunk, when the rotation will cease and the line switching relay 1.4; will at tract its armature.

By opening contact springs 18 and 19, 21 and 22 the line switching relay breaks the circuit of the line relay 13 and by closing contactsprings 19 and 20, 22 and 23 completes a circuit for the line relay 41 and the wiper switching relay 43 of the secondary.

14 of line switch C as follows: ground at G contact springs 63, 62, 61,Iancl 60, bank c'ontact 37', wiper 34, contact springs 25 and 26, windin of line switching relay 14: to battery. he line relay 13 is slow acting,z'. c it retains its armature for an instant after its circuit is broken, thereby allowing time for the establishment of the above described holding circuit. To avoid unnecessary repetition, I will state here-that the line relays 01' all lineswitches, primary, secondary and tertiary, are made slow acting for a similar reason.

A branch of the holding circuit extends over wire 32 (32 in Fig. 6) to the connector group serving the group of lines of which the line of substation A is one, where, by placing ground potential on the multiple test contacts in the connector banks, the line of substation A is made inaccessible to incoming calls.

Returning now to the secondary line switch D. the energization of relay 43 closesthe connection of the wipers 79, 80 and 81 at the contact springs 71 and 72, 68 and 69, 74 and respectively. Also, in connection with the energization of the line relay 11. a locking circuit is completed for relay 13 as follows: ground at G. contact springs 63 and 62. contact springs 65 and 66. windthe operation of the line switch C. i If the .wrpers are standing upon an idle trunk the line switching relay -10 pulls up at once and no rotation takes place. In case the wipers are standing upon a busy trunk the test wiper will find ground potential upon the test Contact, whereby the relay 10 will be short cir cuited and the motor magnet 43 will be energized over the followingscircuit:

ground ontest contact, wiper 80, contact springs 69 and 68, contact springs 56 and 55, contact springsfetti and t7, winding of motor magnet 42 to battery. By interrupting its own circuit at contact springs 46 and 47. motor magnet #12 vibrates its armature thereby rotating the wipers until the test wiper 80 arrives at an ungrounded test contact whereupon the rotation. ceases and the line switching relay 10 attracts its armature? The energization of the lineswitching relay breaks the circuit of the line relay 41 and winding 11 of relay -13 by separating contacts 49 and 50 and 52 and 53 respectively; and, by closing contacts 50 and 51, 53 and 5-1. completes a circuit for the line relay of the tertiary line switch E over the following path: ground at G,

contact. springs 113 bank cdntact.

8T, wiper. 81, contact springs75 and H, contact springs 51 and 153, bankcontact 88, wiper 35, contact springs-23 and 22, subscribersloop, contact 1 springs 19 and 20. wiper33. bank contact 36, contact springs and 51, contact springs 71 and 7'2, wiper 79, bank, contact 85, contact springs 115 and 110, contact springs 100 and 107, winding of 10 relay 90 to battery. This line relay 90 is energized over this circuit and, attracting its armature. completes a new holding circuit as follows; ground at G, contact springs 97 and 96. cont-act springs 111 and bank contact 80, wiper 80. contact s rings 09 and (S8, to cont-act springs 50, 57. 58 and 59,'where the circuit divides, one

' branch extending by way of contact spring 59. bank contact 37, wiper 34, contact springs and 26, and winding of relay ll of line sv'itch C to battery, another branch extending by way ofcontact spring ,58, winding of relay 410, contact springs 16 and v 47, winding of motor magnet- -12 to battery, 25 while a third branch extends by way of contact spring 57, contact springs and (S6,

winding of relay 43 to battery. This holding circuit serves to maintain energized the relay 14 of the line switch C and the relays 40 and 43 of the secondary line switch 1): The energizationof the line. relay 90 of the tertiary line switch E also completes a circuit for the line switching relay 91 and a circuit-for the test wiper 118 which cir- 35 cuits may be traced as follows: ground at G, contact springs 97 and 98, winding of line switching relay 91, contact springs 108 and 109, winding of motor magnet 93 to 1 battery. Test wiper 118, contact springs {0 10]. and 102, contact springs 94 and 95, contactsprings 108 and 109, winding of motor magnet 93 to battery. As in the case of the switches C and D the operation now depends on the condition of the test contact 45 upon which the test wiper 118 is restin j.

If said test contact is ungrounded line switching relay 91 pulls up at once; in. case said test contact is grounded relay 91 is short circuited and the motor magnet 93 59 is energized. Motor magnet 93 interrupts its own circuit at contact springs 108 and 109 thereby vibrating its armature and rotating the wipers until wiper 118 arrives at an ungrounded test contact, whereupon relay 91 is energized and attracts its armature.

lhe line switching relay 91, by separat ing contact springslOG and 107 and closing contact springs 105 and 106, breaks the 0 circuit of the line relay 90 and substitutes thereforthe line relay 135 of the first se lector H the new circuit extending as follows: round at G, previously traced circuit .t rough subscribers loop, contact springs 115 and, 116, contact springs 106 and 105. wiper 120, bank contact 123, :winling otline relay 13,5 tobatte ry. I Upon energizing the line relay 135 closes a circuit for the slow acting relay 129 as follows: ground at Gt", contact springs 118 and 1-17, winding of relay 12) to battery. Upon energizing. relay 1'29 prepares a circuit for the vertical magnet 130, and also completes a new holding circuit as follows: ground at G. contact springs 151 and 150. bank contact 121, wiper 118. contact springs 101, 100 and 99. where the circuit divides, one branch extending by way of contact spring 100 to the previously traced holding circuit of switches C and D, while the other so branch extends by way of contact spring 99, winding of relay 91. contact springs 108 and 109, winding of motor magnet 93 to battery.

The line switching relay 91 also prepares a circuit for the battery B which should be mentioned at this time. It extends from the negative pole of battery 13 bank contact 122, wiper 119. contact springs 101 and 103, to multiple test contactsQGG and 185 in the banks of tinder switches F and t) respectively. The complete circuit of bat tery B will be explained later. I v

The foregoin circuit changes all take place in response to the remo 'al of the rccciver at substation A. We now have one .side of the line grounded at G iirtertiary switch 15, ,while the other side of the line through the windingof line relay 135 ot' the first selector ll, maintaining relay 160 135 energized and, by means of relay 129, controlling a common holding circuit for line switch C, secondary line switch D, and tertiary line switch E. p I

The subscriber at A. may now manipulate his finger dial in accordance with the first digit of the number assigned to substation A, which, since it was assumed that substation A and A are both in the first 10,000 line exchange. is 1. In response to the operation of the finger dial the impulse wheel 8 separates the springs (5 and 7 momentarlly, thereby .decnergizing line relay 1.35 of the first selector H for an instant.

l pon retracting its armature. linc'relay 135 closes acircuit for the vertical magnet 130 as follows; ground at G contact springs 1+8 and 119. contact springs 153 and 152, ofl normal springs l-ll"; and 1 11, winding of slow acting relay 127. winding of vertical magnet to battery. The vertical mag net and the slow acting relay 127 are energized in series over the foregoing circuit, the to-rmer raising the wipers opposite the first level of bank contacts, and the latter 126 completing a circuit for the relay 120 as follows: ground at G". contact springs 141 and 142. winding of relay 1% to battery. Relay 126, in attracting its armature, coinpletcs a new circuit for the vertical magnet, 1.3

relay 127, winding of vertical magnet 130 to battery. Relay 126 also completes a locking circuit foritself as follows: ground at (i contact. springs 151 and 150, contact 134, contact springs 137 and 136, winding of relay 126 to batter The line relay 135 again attracting its arn'iature at the end of the impulse, the' (,ll'Clllt of slow acting relay 127 is broken and an instant later it retracts its armature thereby closing a. circuit for the rotary magnet 1.31 which may be traced as follows: ground at G, contact springs 151 and 150, contact 134;, contact springs 137 and 136, contact springs 142 and 143, contact 133, winding of rotary magnet 131 to battery. The rotary magnet attracts its armature 132 and rotates the shaft one step so that the wipers 15(3, 157 and 158 make connection with the first set of bank contacts of the first level. Xear the end of its stroke the armature 132 opens the contacts 133- and 134 thereby breaking the circuit of the rotary magnet and the locking circuit of relay 126. The rotary armatl'ire, accordingly, falls 1 back; but the deiinergization of the. relay 26 depends on the condition of the test contactupon which the test wiper 156 is now resting. If the trunk with which this test contact is associated is busy, the test contact will have ground potential upon it and a holding circuit for the relay 126 will exist as follows: ground on test contact,

test wiper 156, contact springs 1.37 and 136, winding of relay 126 to battery. Then the relay 126 will remain energized and, as the rotary armature returns to normal position and closes the contacts 133 and 134, the rotary magnet will again be energized and will move the wipers 156, 157-and 158 into connection with the second set of contacts of the first level. in this manner the wipers will continue to be rotated until they reach an idle trunk as indicated by absence of ground on the test con-tact. This time when the contact 13-1- opens the relay 1.26 falls back, thereby opening its own. locking circuit and also opening the rotary magnet circuit \'\'hcreupon the wipers 156, 157 and 158 will be brought to rest upon the set of contacts 162, 163 and 164 of an idle trunk line extending to a second selector K. As a further result of the de'rinergization of relay 126 the impulse circuit extending from the contact springs 149 of. line relay 135 is switched at contact springs 138, 139 and 140 1 ,seaeso from the vertical magnet 130 to the vertical magnet 220 of the second selector K. lVe will now trace'a circuit for the relay 224 of the second selector K as follows: ground at G, contact springs 151 and 150, contact 134, wiper 156, bank contact 162, contact springs 247 and 248, winding of relay 224 to battery. 15y separating contact springs 254 and 263 and closing contact springs 25.3

and 254, relay 224 switches a circuit con1- pleted later by the off normal contact 252, from the release magnet 225, to contact 230'- This circuit will be referred to again. The connection of ground from G to multiple test contacts 162 and 215, also serves to make the second selector K busy to other first selectors-and to the tertiary line switches P.

The subscriber at substation A may now manipulate his finger dial 1n accordance with the second digit of the desired number,

,K, winding of slow acting relay 223, winding of vertical magnet 220 to battery. Im pulses over the foregoing circuit energize the vertical magnet 220 and the slow acting relay'223 in series, the former vibrating its armature in response to the impulses and thereby raising the wipers 255, 256, 257 and 258 until they stand opposite the third level.

The slow acting relay 223 retains its armature in its operated position during the series of impulses and completes an initial energizing circuit for relay 222, which relay locks itself over the following circuit: ground at G, contact springs 244 and 243, contact springs 250 and 251, oit' normal contact 252, contact springs 254 and 253, contact 230, contact. springs 232 and 231, winding of series of impulses, relay 223 'retracts its armature thereby completing a circuit for the rotary magnet which may be traced as a branch of the above locking circuit as follows: contact spring 231, contact springs 241 and 242, contact 229, Winding of rotary magnet 221 to battery. The operation of selecting an idle trunk has been fully described in the case of the first selector H and need not'be repeated. It will suffice to say herethat the rotary magnet interrupts its own circuit at contact 229 and continues to rotate the wipers until the test wiper 255 arrives at an ungrounded test contact when relay 222 to battery. At the end of the the relay 222 is deenergized and the rotacontact springs tion stopped with the Wipers 250- 258 in engagement with the contacts of a trunk line extending to a third selector M.

'We will now trace an energizing circuit for the relay 305 of the third selector M. which was completed by the deencr 'ization' of relay 222. Said circuit extem s, from ground at G, through contact springs 21 1 and 243, contact springs 250 and 251, off normal contact 252, contact springs 25a and 253,

'. contact 230, wiper 255, bank contact 259,

' .tact springs 325 and 324-, winding of motor thereby vibrating its armature magnet 291 of finder switch F, winding of relay 290, to battery. The motor magnet 291 land therelay 290 are. energized over the above circuit, the former interrupting its own circuit at contact springs 324 and 325, and causil'lg wipers 274282 to traverse their respective rowsof bank contacts; and the latter, by closing contact springs 322 and 323, completing a circuit for the test wipers 275, 278 and 281 as follows: positive pole of battery B (Fig. 4), wiper 157, bank contact 163, wiper 256, bank contact 260; winding 296 of test relay 295, contact springs 322 and 323, to testwipers 275, 278 and 281. The negative )ole of battery B has already been traced tl irough contacts in tertiary line switch E to the test contact 266 and its multiple contacts in the banks oi finder switch F and other finders. It is evident, therefore. that when the test wiper 275 arrives at the test contact 266 the circuit of the battery 13 will be con'ipleted through the winding 296 of test. relay 295. Test relay 295 attracts its armature and by separating contact springs 337 and 33S, interposes its own high resistance winding 297 in the circuit of motor magnet 291 and relay 290 thereby locking itself and causing motor magnet 291 and relay 290 to become inoperatire.

stops with wi 'iers 274, 275 and 276 l'esfi'ng upon bank contacts 265,266 and 267;"these contacts being the multiple termi nals of the trunk line selected by the secondary line switch D. Wipers 277, 278 and 27 9 remain open for the present at the side switch contacts.

1 The subscriber at substation A may now call the third digit of the. desired number .which is 1, resulting in a momentary deenergization ofline relay 135 of the first which -,Sends an impulse to the .from ground at G.

The rotation of the wipers accord contact is reached.

vertical magnet of the third selector M over the following path: ground at G" contact springs 118 and 149, contact. spriz'igs 155 and 152, 06' normal springs 116 and 145, contact springs 139 and 110, wiperlfiS, bank contact 16%, oil' normal springs 239 and 238 of second selectordx contact springs 235 and 256, wiper 258, bank contact 262, contact s1.)rings 331 and 330, winding of slow acting relay 309, winding of vertical magnet 5111 to battery. "The vertical. magnet 311 and the slow acting relay 369 are energized over this circuit, the former raising the wipers 14.10

and 111 until they stand opposite the first level and the latter closing a. circuit for the relay 319 andrelay 316 as follows: grouinl at G contact springs 33% and 382, winding of relay 319, winding 318 of relay 316 to battery. l'pon energizing, relay 319 co1npletes a locking circuit for itself and relay 316 which may be traced. as a branch of thc holding circuit of rilay 365 extending extends from contact spring 358, through contact 375, contact springs 386 and 387, winding of relay 319, winding 318 of relay 316 to battery. Relay 316 upon. energizing, connect-s up the wipers 110 and 411.

At the end of the impulse the slow acting relay 309 deencrgizcs and completes a circuit for the rotary magnet 310 which maybe traced as a branch of the above described locking circuit of relay 319 as follows: contact spring 387, contact springs 382 and 381, contact 376, winding of rotary magnet 316 to battery.v Rotary magnet 310 is energized over this circuit and attracts its. armature 321 thereby rotatin the wipers 419 and 411 until they engage the first set oi contacts of the first level. Near the end of its stroke the rotary armature 321 breaks the contacts 375 and 376 thereby opening fihe rotary magnet circuit and the locking circuit of relays 319 and 316. The rotary magnet deencrgizcs and retracts its armature but the delinergiZation of relays 319 and 316 depends upon the condition otthe test contact upon which the test wiper 110 is now resting. It the trunk with which this tcst contact 'is associated is busy it will-harc ground potential upon'it and a holding circuit for relays 2-319 and 316 will be eli'cctivo over the following path:

-. gloln'ld' on test contact, test wiper 410, con- The branch circuit ifore, tllatas longas the test and rotaryanagnet 310 will continue rotat ing the wipers until an ungrminded test Then, as contact 375 opens, relay 319 deenergizes, breakin the rotary magnet circuit and stopping the rota.-

tion. Relay 316, however, does not deiinergize but is locked over a new circuit which may be traced as another branch of the holding circuitof relay 305 as follows: contact spring 358, contact 375, contact springs 396 and 395, winding 317 of relay 316, contact springs 403 and 402, wiper 410, contact 412, winding of relay 420 of connector N, contact -sprin, ;s 439 and 440, winding of relay 421 to battery Before continuing with the operation of connector N it will be necessary to return and consider the operation of the side switch wipers 283, 284 and 285. At the end of the impulse or series of impulseswhich operate the vertical magnet. of third selector M, the slow acting relay 309 retracts its armature and completes, in addition to the rotary magnet circuit already described, a circuit for the private magnet 320 which may be traced as a branch of the locking circuit of relay 295 as follows: contact springs 337 and 336, contact springs 379 and 380, contact springs 388 and 389, winding of private magnet 320, oli' normal springs 37 8 and 377 (closed at first movement of shaft) to battery. The private magnet interrupts its own circuit at contact springs 388 and 389 and is made slow acting so as not to work too fast. At each denergization of the private magnet. its side switch wipers 283, 284, and 285 are shifted to their next position in the well known manner. Vhen the side switch levers reach their second position the circuit of battery B will again be completed over the same path as before except that winding 293 of test relay 292 and side'switch wiper 284 are substituted for winding 296 of test relay 295 and contact springs 322 and 323. The test relay 292 is energized over the above circuit and attracts its armature, thereby separating contact springs 326 and 327, breaking the locking 'circuit of relay 295, and interposing its own high resistance winding 294 in the circuit of the private magnet 320, thereby locking itself and cans .ing the private magnet to become inoperative, the side switch levers remaining in their second position. By bringing contact springs 332 and 334 into engagement with contact spring 3331 2Llld 335, respectively, test relay 292 completes the circ it 01" the double wound line relay 302 of third selector M over the following path ground at G, winding 303 of line relay 302,contact springs 346 and 347,contact springs 334 and-335, side switch wiper 285 in its second position,

-wiper 276, bank contact 267, previously traced circuit through subscribers loop, bank c0ntact'265, wiper 274, side switch wiper 283 in its second position, contact springs 332 and 333, contact springs 344 and 343, w lnding 304 of line relay 302 to battery. The line relay 302 energizes over the above circuit and, attracting its armatare, completes the circuit of slow acting relay 306 as follows: ground at G, contact springs 356 and 355, contact springs 390 and 391, contact springs 400 and 399, wind- '4.) to battery. Relay 92, attracting its airmature, closes contact springs 110 and 112 and separates contact springs 110 and 111, thereby disconnecting ground at Gr from the holding circuit extending to the line switches C and D and substituting therefor ground overthe previously described -fiergizing circuit of relay 92. Relay 92 also separates contact springs 113 and 114 and contact springs 115 and 116, thereby removing ground at G from one side of the trunk line and disconnecting the other side of the trunk line from the line relay 135 of the first selector H.

Upon the denergization of line relay 135, the circuit of slow acting relay 129 is broken and it denergizes, closing contact springs 153 and 154 and thereby energizing the release magnet 128 which restores the first selector to its normal position in the well known manner. The dci nergization of relay 129 also separates contact springs 150 and 151 thereby breaking the holding circuits extending to line switching relay 91 of tertiary line switch E and relay 224 of second selector K. The denergization of line switching relay 91 disconnects the wipers 118, 119 and 120, thereby freeing the trunk line to the first selector H and makin its accessible to other calls.

The relay 224, upon deie'nergizing, closes contact springs 254 and 263tl1erebyco1npleting the circuit of the release magnet 225 which energizes and restores the second selector to its normal position in the well known manner. The separation of springs 253 and 254 of relay 224 disconnects ground at G- from two holding circuits e'xtending to contact springs 358 and 327, re

spectively, where they have been previously traced: These holding circuits, however, have already been connected together at. contact springs 327, 328 and 329 andto ground at G by the energization of slow acting relay306 and consequently they remain effective:

The slow acting relay 306, when en ized u )011 the o )eration of line rela 302 as previously described, separated the contact springs 361 and 362 and contact springs 358 ret-as lot third selector M.

one step past the escapement 3t).

and 359, the former opening the circuit of the release magnet 308 at a new point and the latter breaking the circuit of the relay 305 which deenergizes. Upon the deenergization of relay 305, contact springs itii and 368 are closed but contact springs 30% and 365 are held open by the engagement of tinger 366 with the escapement 563 controlled by slo acting relay 307.

To sum up the operations so far, the calling line has been extended through primary line switch C, secondary line switch D, and finder switch I to the line relay 302- ot the The third selector M has been operated, by way oi the first selector H and the second selector K to select a trunk line to an idle connector N and these selector switches have been restored to normal.

The subscriber at substation A may now operate his dial in accordance with the fourth digit of the desired number thereby breaking the continuity of his loop a number of times at the impulse springs (3 and 7. As a result the line relay 302 of the third selector M is momentarily decnergized a corresponding number of times and sends a series of impulses to the vertical magnet 422 of the connector N over the following path ground at (:l, contact springs 355 and 35+, contact springs 361 and 360, winding of slow acting relay 307, ontact springs 6L0?) and 40-1, wiper 411, bank contact 413, side switch wiper 448 in its first position, winding of vertical magnet 422, winding of the; slow acting relay 426 to battery. The vertical magnet operates in response to these impulses to raise the two sets of wipers 451-452 and 453t54 until the latter set stands opposite the tens level in which are located the normal contacts of the desired line. Slo acting relays 307 and 426 are energized in series with the vertical magnet and retain their armatures during the series of impulses.

Relay 4'26 completes an energizing circuit for the private. magnet which is broken at the end oi the series of impulses thereby allowing the side switch wipers 4-1-8, 4-19, and 4500) move to their second position in the well known manner. The operation oi? the relay 307 allows the finger acc to move The subscriber at substation A may now operate his dial in accordance with the last digit of the-desired number resulting as before in separating the springs T and H a correspomling number 01 times. The line IIJIJ to the last digit of the desired number when the wipers 453 and's ot will rest upon the normal contacts of the desired line. It is understood that the other set of wipers -51 and'oz'z are also resting upon the same numbered contacts in the other bank but these wipers are disconnected by the wiper switching relay 420. If the wipers of the third selector had been raised to the second level instead of the 'first the wiper switching relay 420 would not have operated and the set of wipers +51 and would be left in service. 1

Now at the end of the last series of impulses the slow acting relay 4% retracts its armature dei ner izino the )rivate ma net (assuming the called line to be idle.) and allowing the side switch wipers &8, +49 and 450 to move to their third position. Also the slow acting relay 307 retracts its armature, operating the escapement 362 and allowing the contact springs 36% and 365 to close. \V'e may now trace the negative pole of battery B through side switch wiper 448 in its third position, bank contact 413, wiper 4-11, contact springs 40+ and 405, winding 315 of relay 313, contactisprings 365 and 364-, to test contact 83"and multiple test contaGts in the banks of secondary line switches I) and similar secondary switches. It will be shown later on how this circuit is completed to the other pole of battery B.

\Ve may now trace two circuits extending over the normal wires 31 and 32, to the line switch (1. The first of these to become operatively efiective extends from the ground at G 'g through contact springs 435 and 434, contact springs 42!) and 430, side switch wiper 449 in third position, wiper 45+,bank contact 458, normal wire 31 to one side of the line of substation A whence it passes by way of contact springs 19 and 1S and the winding of line relay 13 to battery. The line relay 13 is energized over the above circuit whereupon the line switch (1 operates to rotate its wipers 33, 3.4. and 35 until they rest upon contacts of a trunk line leading'to an idle secondary line switch I). The operation is the same as that already described in the case of the line switch t. A holding circuit for the line switching relay ll may be traced from the connector X as follows: ground at G, contact springs HT and 4-16, contact springs 4-H and 443, re-

sistance r. contact springs 432 and 433,,

wiper i473, bank contact 457, normal wire The lines oi substation A and the norma] wire 32 have, now been extended to secondary line. switch lli. Bearing in mind the fact that the two normal wires are still grounded at the comiector N. a circuit for the line relay 41 of secondaryline switch i) may be traced as follows: ground on normal wire 31. contact springs 19 and 20', wiper i5 5, bank contact 3 3, contact springs .30 andiflfl winding of line relay 4:1 to battery. A branch of the abo e circuit goes through winding of motor magnet l over the. 'i'ollowing path: contact springs 50, or and l contact springs 67 and (38' contact springs 5e and 55, contact springs as and i7, winding oi motor magnet +2 to batrel-y.

The line relay 4-1 and the motor magnet 42 are energized over the above circuit, whereupon the switch starts rotating in search of the trunk extending to the third selector M. it will be seen that, inasmuch as the secondary switch D is being operated by a ground on the negative. line 12. no current. will flow in the winding l-t of the relay 4-3 and this is true even it the sub scribe-r at A should remove his receiver while switch D is rotating. Consequently relay '3 is inoperativeand the wipers 76, T? and T8, are made active while wipers 7!). so, and 81 (used in the case of the calling secondary switch D) remain disconnected.

li e may now trace a circuit of the positive polo oi battery ld 'as follows: positive pole of battery R, contact springs 432 and 433. wiper 11523. hank contact lfiT, contact springs so and :25. wiper EH, bank contact 37, contact spring 50, contact springs (30, (31 and 62, contact springs (mama 64- to test wiper 77. The negative, pole of battery B has already been placed to the multiple test contacts such as HP, ot the trunk leading to third selector M. ll'hen, therefore, the test wiper T7 arrives at the contact 8?) the circuit of battery ll will be completed through winding 315 of relay 313 ot the third selector hi. Relay 313 energizes over the above. circuit and locks itself through its high resistance winding Elli as follows: ground at (W, contact springs 357 and 35S, contact 37;). contact springs 396 and 239i, contact springs illl and 340, winding ill I oi relay 313 to battery. By separating contact springs 39S and 396. relay 313 31H? relay til). and relay +21.

ltelay ill, by retracting its armature, re moves ground from side switch wiper H9 thereby stopping the rotation of secondary line switch i) and allowing line switcln iug relay it) lo energize (since it is no longer short circuited) and lock itself over a holding circuit extending from the third selector over the i'ollow iug path: ground at G, contact springs Z357 and 35m, re -l mm breaks the circuit of winding ill? of relay r, bank contact 83, wiper 77', contact springs 6t and (35, Contact springs 57 and 5S, winding of line switching relay 4A) to battery. A branch of the above holding circuit may be traced from contact springs 57, 58 and 59, by way of bank contact 37, wiper 2-3-11, contact springs 25 and 26, and winding of line switching relay ll to battery. Another branch extends, as already explained, over normal wire 32 to multiple test contacts such'as 457 where, after connector N is released, the line of substation A is made busy to other. calls. The release of the connector N takes place as soon as the relay 421, by retracing its arniali-urc,

completes the circuitof the release magnet 42st. The release magnet 42$ upon energizing, restores the side switch wipers H8, ll!) and 450, and the shaft to their normal position in tho'regular manner. Furthermore the connector N is made accessible to other calls by the detinergization of relay 316 whereby the third selector wipers 410 and 411. are disconnected.

The line-of substation A has now been extended through the medium of line switch C and secondary line switch D, to the third selector M where there is bridged across it the double wound back bridge relay 295) in series with the battery as follows: ground at G", winding 301 of relay 29$),contact springs 353 and 352,'bank contact 84 wiper 78, contact springs 73 and Ti, contact springs 5i and 52;, bank contact 38, wiper 35, contact springs 23 and 22, wire 11, through subscribens loop, wire 12", contact springs 19 and 20, wiper 33, bank contact 36', contact springs 50 and 51. contact springs 71 and TO, wiper To, bank contact 8'2,

coiitact springs 349 and 350, winding 300 of relayilt ll to battery. This is the circuit over which talking battery is fed to substation A, although, since the receiver is on the hook, no current will flow as yet.

lle may now trace a circuit for the ring.- ing relay 2% which was closed by the relay 313. This circuit extends from ground at G, through interrupter I, contact springs 39? and 398, winding of ringing relay 298 to battery. The ringing relay is energized interinittmitly and operates to disconnect the line of the calledsubstation from the back bridge relay and to connect it with the ringing current generator Gen .tor the purpose of signaling the called subscriber.

llhen the subscriber at substation A removes his receiver from the hook, the ringingirelay being momentarily inactive, the

previously described circuit of the back bridge relay is completed and the Said relay attracts its armature thereby reversing the line of substation A at springs 842- 3=l7 thereupon deenergizes and opens the circuitof the "ringing relay at contact springs Karation of contact springs 399 and 400, (re-- and 39s. p

. A complete talking circuit has now been established between the substation A and the substation A and is indicated in the drawings by the heavy lines. The connecnormal may be accomplished by hanging tion is controlled by the calling subscriber bynieans of relay 302 which in turn controls relay 306 which, by holding contact springs 3'57 and 358 together, supplies a, holding ground to all the switches in multiple over circuits which have been explained.

The restoration of all the apparatus to up the receiver at ,su-bstation A thereby relay 302 denergizes and opens the circuit of slow acting relay 306, which deenergizes in its turn and, by separating contact springs 357 and 358,1'emoVes the holding ground extending to finder switch F, tertiary switch E, secondary line switch D, primary line i switch C, secondary line switch D, and

primary line switch 0, whereupon the several relays locked up in these switches are Also, by closing contact springs 361 and 362, the circuitof the release magnet 308 is completed, resulting in therestoration of the side switch wipers and theshaft of the third selector M, to

their normal .position in the well known manner. Whereupon all the apparatus W1ll-- have been returned to normal and made ready for use in extending another connection.

'I will now describe briefly the operations that take place when the called line is busy. It has been explained how at the end of the last series of impulses sent to the connector N the. wipers 453 and 454 will be brought into engagement with bank contacts 457 and" 453 these being the normal contacts of the line extending to substation A. Now if the line of substation A is busy, test contact 457 will have ground potential upon it, where-by, upo'n the denergization of slow acting relay 426, a locking circuit s established for the private magnet 427 as follows: ground on test contact, wiper 453, contact springs 433 and 432, resistance 1'', contact springs 433 and 434, contact springs 446 and 445, winding of relay 425, winding of private magnet 427 to battery. The private magnet remains energized over thls C11- cuit thereby holding the-side switch wipers in their second position. Relay- 425 is energized in series with the. private magnet 420 and 316. Upon the-denergization'of relay 421, the circuit of the release magnet V .424 is completed and the connector N is restored to normal. .Uponthe deenergization of relay .316 the shunt path around busy. re-

y 312 is broken momentarily byt P:

391 are opened before contact springs 400 and 401 close. Relay 312 is now locked up 111 series with relay 306. A distinctive tone from the transformer T and busy machine It may be S is now projected out over one side of the calling line by th closure of c ontact springs 392 and 393, whereby the calling subscriber is informed that the desired line is lusy and therefore inaccessible for the time being. The calling subscriber may now hang up his receiver, thereby bringing about the re- .storation of the apparatus to normal in a manner substantially as previously 'described.

I will now describe the operation of trunking between two 10,000 line exchanges. Each interoifice trunkhas at its outgoing end a repeater R and finder switch 0, and at its incoming end a line switch P. The

finder switches 0 have access to the trunksextendingfrom the banks of secondary line switches D to the banks of finder switches F, and'are themselves accessibleto first se-v lectors such as H. The line switches P have access to second selectors such as K and are themselves accessible to finder switches F.

Referring to Figs. 4, 5 and 6 we will assume that the apparatus shown in Fig. 4

' is located in one exchange and the apparatus shown in Figs. 5 and 6 in another exchange, and we Wlll furthermore assume that the. outgoing trunk shown near the lower right hand corner of 'Fig. 4 terminates in the incoming trunk shown in'the lower left hand corner of Fig; 6. This trunk is indicated at its outgoing'and in-' coming ends by reference characters 520 and 521. In the followingdescription I will cover in detail only that portion of the operation which differs from the operation already described.

When the subscriber at substation A removes his receiver he is connected through the successive operations of line. switches C, D,fand E with the first selector H. He may now operate his dial in accordance with the first digit of the desired number which is 2, whereupon the wipers of the first selector H are raised until they stand opposite the second level and are then automatically rocontact 134, wiper 156, bankcontact 159,- winding 1700f relay 163. contact springs 180 and 17 9, winding of inotor magnet 167 Tim moiur 11mg}- ne s MT is mirry ixwl uml 5mm i'()i21illl,1'illi WllHPl'S 181. l. ILEHl 15 3 in riz'zn'fll hi lhr. trunk lino upon \rhirh Lhv mx'lin iripm'ie ml? SQCURKlIUTy lino switch 1) 11w ithi'lllgl. it has hem] previously lxXPifllllkli huw (hr i og'utim 1min of butter ,l"is wihwulwl through tertiary linu HWlMl) i i (0 lhv tr al whim-t 183 and its mulliplo twat ((Hliiii'iH. The pnsiliru pole of butler} i may now l)( inn-ml h way of wiper L57. lnglili mntmi J50. winding; 16 (if rvhly 16H in hes. wipvr KHZ. it is evident, lliorvi'nrv, that when the tesi; wiper 18:2 arrives at h s; rmmlcl' 185 the circuit of lltltl(i B will lw cumplrmi iilinllgfll winding U39 hi rvlny fil'm. hmhly 16h euergizes iwrr lhv ulmwc rim-nil and. h)" supurutingr colltairl' springs 1.7T null 179, interposos its high I'Ufjlmi'ilhfik whirling iii) in the circuit of the rntury iimg'iwl' thurvh lurking itself and stripping the rnrzition with the Wipers 191., 151;. will 1H3 mating on (10H- uicts 184-, i555 21ml 1Hl' rv:-;p rti\'0l By lii'ingiiap; whim: spriw i zlml 173 into ungzigxmnrnf \Yiill rmihict and Lil, L'LEr wrliwly, rvlzly 113:5 completes the (:irciiil; 0, ilw lino relay 43W.) uiiihe r0- mm .11 as *iwllmm: ground t-lll (ih winilihg 502 of H110 rrlny 5W. contactsprings 1H and 173, wiper 1H1, miilmsl 184., prm'iiiusly trzu'ml. ('liCllli' including hllllfiitliiull A, bank contact, LSlL i'vipvr lS-i. contact springs 1'53 11ml 1T2, winding 501 0%? lim-z relay Bill) to battery. Linv Win 500 is riiijergizciail ever the ihm'v virwuii 11ml unnplo an energizing (ii-Quit 'lur ahiw :iriilng rvl: 50?, lliiilzly 50? :iitrnifl' its zirhmuiru zlll i rompleios ea, circuit for l'l:l:l 9; of fer Ir) llim ".tch 11 us 'ln'llows: g: immi. iii? (W mhlzici :5

new hi3 f :1 path which has; 130011 prvvio: 1:.

D9011 the (*lMflQiZililUll 05 line whiy 430%) :1 circuit, is z lsn C(Hllilii' fli, fur the, sin

iiiw- Y the ing' linev relay {ill 0 the distant eJchungw springs 17:5

winding (12' relnrilutima (mil 51), wire 52L miilzuxl springs Eli and 211 rmitaicr springs 20% 21ml 20.1 \.'li1(ll11jf oi linev ruhw .190 in huttvry. Thv Awfacling Jim: ra a5 19 i pmr ;\H1'2lc'Ei1l.;I ils :iiiimturv, completes :1 rn'rml i'm' ihu linu Wil'ClliilSf rcizw llll .zmci :1 virruit for the M5! wiper l lir former (*xlrmling tlrmzi grimml at (3 hy W213 0%? runtzict rapring'fi 1.96 and 197, Winding or rrluy 19L conl'nrt springs 206 and 20? and winding of nm'mr magnet 19:2 To batterv; and (he hitter exirmiingi' from test; wipm Zia by Way 01 pcnl'uri 'priiu 199 ami 260, :Liliil QUlliilt'i' springs 1% and i in contact spring 206 whvre the two (ii'kilii's jail in Chi: test wiper :31! is resizing llpfifl the, 5195!; c011- izirt m"; a busy trunk line it will. find round pQiL-iitinl thvre, and the circuit 0'5? iha: first wiper will actas n Ishori circuit for lhe ri in 91 prm'iili. at the same ltime u. slirrul gronmi for tha mom]- mz'aggiiat The izi0- $01 hizigiiei 3.552 'therrupmi operates in r 1- l the 110 line rrlu) :22? iii. seimriil :avlmrir h (arr-r tie iuliowi pzvih: ground HIP mutual; and, 20! ml 'l'rucml 0 kill? in er Wires 520 :liiil izi sprinm L10 and '21, coi'ztzurl; spri 53M and 203 wiper 2H. mill: C(lililiwl; (i m5; 0f lino rainy 2:57 r ifil"; l slziy 22'?" is energized m'i'ar (ha ill: and, by (losing :hniiiCi/ s n-i1 Lill- :mal 2&5. wiiigplazl'es m ine y; cirrfmiv mi FiiOW art 121;; remjr 2% which .i y *on attractin its; illiliiiillliffi, cmiiplr' Q circuit, relay 191 0% lim: "iwl. 'me 0 0 sgrrmmi umii'iaici .wwings JG, 12 3- mid 25H" m hat/tin" 0Y0 vii-(suit hm Operation 7 7 clear. l mthe 'circuis has 110W 390D. iwl'zihlishz ii liar 4 r i 31% m le] -21. warm: springs. 

